High integration or high-density packaging has been increasingly accelerated in recent years as semiconductor packages widely used in electronics, communication devices, personal computers, etc. have been more highly functionalized and/or miniaturized. Along with this, diverse requirements are imposed on laminates for use in such semiconductor packages. In addition to heat resistance and reliability, various characteristics such as low thermal expansion, high heat conductivity, and high elasticity have been demanded.
Among them, particularly, laminates having low thermal expansion have been strongly desired. This is due to the following factor: a semiconductor device and a printed-wiring board for a semiconductor plastic package largely differ in the coefficient of thermal expansion, and this difference in thermal expansion causes the warpage of the semiconductor plastic package upon application of thermal shock during the production process. As a result, poor connection occurs between the semiconductor device and the printed-wiring board for the semiconductor plastic package or between the semiconductor plastic package and the on-board printed-wiring board. Accordingly, the laminate having low thermal expansion is used with the aim of minimizing such difference in thermal expansion.
In addition, high heat conductivity has also been strongly desired for laminates in recent years. This is because an opportunity to use semiconductor plastic packages in high-temperature environments has been increased as indicated by, for example, research on the mounting of engine control units on automotive drive divisions, or because the amount of heat generation is increased due to an increased number of parts to be installed in association with high integration or high-density packaging. Approaches such as studied heat sinks or radiation fins and laminates equipped with thermal vias have been adopted as countermeasures against heat. These approaches, however, are less than sufficient. Thus, higher heat conductivity has been demanded for enhancing the radiation of laminates themselves.
A method which involves filling of a high proportion of a filler excellent in various characteristics is known as a method for imparting low thermal expansion or high heat conductivity to laminates (see e.g., Patent Documents 1 to 3). Also, the high filling of the filler is used as an approach useful in the high functionalization of laminates, because this approach can not only impart low thermal expansion or high heat conductivity to the laminates but improve mechanical characteristics (e.g., modulus of elasticity), resistance to burning, electric characteristics, and whiteness.